Re: optics/Japan

[David Dockstader <DRDOCK00@UKCC.UKY.EDU>]

On Thu, 06 Nov 1997 07:44:37 -0600 brian whatcott said:
> >
> I was surprised by the resolving power of the optics you mentioned.
> In the modulation tranfer function plots I am familiar with ( for cameras)
> the resolution limit seems to occur around 300 line(pairs) per mm
> at perhaps 5% modulation, with a more representative value of 180 lpmm
> for reasonable modulation depth.
Where did these MTF plots come from?  What were they supposed to represent?
I've looked at a lot of lenses and I can tell you for a fact that any lens
that cuts off at 300 lines/mm isn't much of a lens.  Perhaps the MTFs that
you have also included the effects of the film.  Another possibility is that
they were for a lens stopped down to f5.6 or so.  (Of course for a long
telephoto or a large format lens f/5.6 may be all you get.  My comments
above were for moderate focal length lenses for a 35 mm SLR.  A general rule
of thumb is that the resolution of a diffraction limited lens should be
around 1800 divided by the f#.  This is for the lens only and does not allow
for degradation (or enhancement) by film.